Drill bit and cutter element having multiple extensions

ABSTRACT

A cutting element is disclosed having multiple cutting extensions extending from the base portion and separated by valleys. The cutting extensions of the cutting element include both crested and rounded shapes. The cutting extensions may differ in extension height, shape, extension angle, cant angle, and crest angle in other characteristics such as in material properties such as wear resistance, hardness and fracture toughness. The cutting elements have particular, but not exclusive, application in the nose portion of the cone cutters of a rolling cone bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/113,747 filed Apr. 25, 2005, entitled “Multi-Lobed Cutter Element for Drill Bit;” which is a continuation application of U.S. patent application Ser. No. 10/355,493, filed Jan. 31, 2003, entitled “Multi-Lobed Cutter Element For Drill Bit;” this application is also a continuation-in-part application of U.S. patent application Ser. No. 10/371,388, filed Feb. 21, 2003, entitled “Drill Bit Cutter Element Having Multiple Cusps.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The invention relates generally to earth-boring bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. More particularly, the invention relates to rolling cone rock bits and to an improved cutting structure for such bits. Still more particularly, the invention relates to enhancements in cutting element design.

BACKGROUND OF THE INVENTION

An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by revolving the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole toward a target zone. The borehole formed in the drilling process will have a diameter generally equal to the diameter or “gage” of the drill bit.

A typical earth-boring bit includes one or more rotatable cone cutters that perform their cutting function due to the rolling movement of the cone cutters acting against the formation material. The cone cutters roll and slide upon the bottom of the borehole as the bit is rotated, the cone cutters thereby engaging and disintegrating the formation material in the bit's path. The rotatable cone cutters may be described as generally conical in shape and are therefore referred to variously as rolling or rotary cones, cone cutters, or rolling cone cutters.

Rolling cone bits typically include a bit body with a plurality of journal segment legs. The rolling cones are mounted on bearing pin shafts that extend downwardly and inwardly from the journal segment legs. The borehole is formed as the gouging and scraping or crushing and chipping action of the rotary cones remove chips of formation material which are carried upward and out of the borehole by drilling fluid which is pumped downwardly through the drill pipe and out of the bit.

The earth disintegrating action of the rolling cone cutters is enhanced by providing the cone cutters with a plurality of cutting elements. Cutting elements are generally of two types: inserts formed of a very hard material, such as tungsten carbide, that are secured in apertures in the cone surface; or teeth that are milled, cast or otherwise integrally formed from the material of the rolling cone. Bits having tungsten carbide inserts are typically referred to as “TCI” bits, while those having teeth formed from the cone material are commonly known as “steel tooth bits.” In each instance, the cutting elements on the rotating cone cutters break up the formation to form new borehole by a combination of gouging and scraping or chipping and crushing.

In oil and gas drilling, the cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed before reaching the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string as been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which must be reconstructed, section by section. As is thus obvious, this process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is always desirable to employ drill bits which will drill faster and longer and which are usable over a wider range of formation hardness.

The length of time that a drill bit may be employed before it must be changed depends upon its ability to “hold gage” (meaning its ability to maintain a full gage borehole diameter), its rate of penetration (“ROP”), as well as its durability or ability to maintain an acceptable ROP. The form and positioning of the cutting elements (both steel teeth and tungsten carbide inserts) upon the cone cutters greatly impact bit durability and ROP and thus, are important to the success of a particular bit design.

The inserts in TCI bits are typically arranged in circumferential rows on the rolling cone cutters. Most such bits include a row of inserts in the heel surface of the rolling cone cutters. The heel surface is a generally frustoconical surface and is configured and positioned so as to align generally with and ream the sidewall of the borehole as the bit rotates. The heel inserts function primarily to maintain a constant gage and secondarily to prevent the erosion and abrasion of the heel surface of the rolling cone.

In addition to the heel row inserts, conventional bits typically include a circumferential gage row of cutting elements mounted adjacent to the heel surface but oriented and sized in such a manner so as to cut the corner of the borehole. Conventional bits also include a number of additional rows of cutting elements that are located on the cones in circumferential rows disposed radially inward or in board from the gage row. These cutting elements are sized and configured for cutting the bottom of the borehole, and are typically described as inner row cutting elements.

Typically positioned on or near the apex of one or more of the rolling cone cutters, are cutting elements commonly referred to as a nose cutter or nose row cutters. Such cutters are generally responsible for cutting the central portion (or core) of the hole bottom. They may be positioned as a single cutter at or very near the apex of the cone cutter, or may be in a circumferential row of several cutting elements disposed near to the cone apex.

Earthen formations generally undergo two types of fractures when penetrated by a cutting element. A first type of fracture is generally referred to as a plastic fracture, and is a fracture where the cutting element penetrates into the rock and volumetrically displaces the rock by compressing it. In this circumstance, shearing or tearing fracture, rather than tensile fracture, is the major mode of crack propagation. A plastic fracture generally creates a crater in the rock that is the size and shape of that portion of the cutting element that has penetrated into the rock.

A second principal type of fracture is what is referred to as a brittle fracture. A brittle fracture typically occurs after a plastic fracture has first taken place. That is, when the rock first undergoes plastic fracture, a region around the crater made by the cutting element will experience increased tensile stress and will weaken and may crack in that region, even though the rock in that region surrounding the crater has not been displaced. This region of increased stress is generally recognized as the “Hertzian” contact zone. However, in certain formations, when the cutting element displaces enough of the rock and creates enough stress in the Hertzian contact zone adjacent to the plastic fracture, that rock in the region of increased stress may itself break and chip away from the crater. Where this occurs, the cutting element effectively removes a volume of rock that is larger than the volume of rock displaced in the plastic fracture.

The characteristics of these fractures depend largely on the geometry of the cutting element and the properties of the rock that is being penetrated. In general, for a given formation, a sharper insert will generally create more of a plastic fracture whereas a more blunt cutting element will produce more of a brittle fracture. The more blunt insert will typically require a higher force, however, to penetrate to the same depth into the rock as compared to a sharper cutting element. Because a brittle fracture generally removes more rock material than a plastic fracture, it is advantageous to provide a cutting element suitable for inducing brittle fractures and that performs that function without requiring increased force or weight on bit. Thus, to increase a bit's rate of penetration (ROP), it is desirable to increase the bit's ability to initiate brittle fractures at the locations where the cutting element engages the formation material so that the volume of rock removed by each hit or impact of the cutting element is greater than the volume of rock actually penetrated by the cutting element.

A variety of different shapes of cutting elements have been devised. In most instances, each cutting element is designed to optimize the amount of formation material that is removed with each “hit” of the formation by the cutting element. At the same time, however, the shape and design of a particular cutting element is also dependent upon the location in the drill bit in which it is to be placed, and thus the cutting duty to be performed by that cutting element. For example, in general, heel row cutting elements are generally made of a harder and more wear resistant material, and have a less aggressive cutting shape for reaming the borehole side wall, as compared to the inner row cutting elements where the cutting duty is more of a gouging, digging and crushing action. Thus, in general, bottom hole cutting elements generally tend to have more aggressive cutting shapes than heel row cutters.

In many conventional TCI bits, conventional nose row cutters are typically of the chisel-shaped or conical designs. A chisel-shaped insert possesses a crest forming an elongated cutting edge that impacts the core portion of the hole bottom. It is particularly suited for softer formations. By contrast, as compared to a standard chisel-shaped cutter, a conical insert is considered less aggressive as it has a relatively blunt cutting surface, and does not include the relatively sharper cutting edge formed by the chisel's crest. As such, the conical design tends to be more durable than the chisel-shaped cutting element, particularly in harder formations. Regardless of its shape, conventional nose row cutters will only contact the core approximately 1.25 times per bit revolution. At the same time, due to their greater numbers, a row of cutting elements in other locations on each cone contact the hole bottom with much greater frequency, thereby removing formation material faster than at the borehole center. In certain formations, this may result in a core of material that remains uncut and builds up in the center of the borehole, causing the drilling of the borehole to be slower and more costly.

Accordingly, there remains a need in the art for a cutting element with a cutting structure that will allow it to remove more material from the hole bottom, and in particular—the hole core, with fewer revolutions of the bit. Such an enhanced design would hopefully provide a higher ROP and an increase in the footage drilled. It would be desirable to provide cutting elements designed and oriented so as to enhance brittle fracture of the rock formation being drilled, and to present to the formation multiple cutting edges as the cutting surface of the cutting element rotates through its cutting trajectory so as to take advantage of multiple cutting modes. At the same time, however, the cutting element should be able to withstand drilling in multiple formations as typically encountered when drilling with TCI bits. Thus, the desire for a more aggressive cutting element must be tempered by the need for providing a durable and relatively long-lasting cutter, one that will resist breakage.

BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the invention are disclosed which provide an earth boring bit and cutting element design intended to provide the potential for increased ROP, as compared with bits employing cutting elements of conventional shape. The embodiments disclosed include cutting elements having aggressive cutting surfaces that have particular, but not exclusive, application in the nose region of a rolling cone cutter.

In one preferred embodiment, a cutting element for a drill bit includes a base portion and a cutting portion having two or more cutting extensions extending away from the base portion, and having valleys between the cutting extensions. The cutting surfaces of the various cutting extensions of the cutting element may be different in shape, or uniform in shape, and may have different extension heights. The cutting extensions may be crested extensions, such as extensions having a chiseled-shaped cutting surface. Further, with respect to crested cutting extensions, such cutting extensions include crests that may differ in crest length, and may form angles relative to the cutting element axis. The angles, referred to as twist angles or crest angles, may be the same or different for different cutting extensions on the cutting element. Further, the cutting extensions define extension angles relative to the longitudinal axis of the cutting element. The extension angles among the plurality of cutting extensions, of a cutting element, may differ, or may be the same. One embodiment includes a cutting element wherein the cutting portion includes a plurality of cutting extensions configured and arranged such that the cutting element includes an asymmetrical cutting surface. In certain embodiments, the cutting extensions are canted and may differ in cant angles.

In certain embodiments, the cutting portion of the cutting element includes a foundation surface adjacent to the base portion, and the cutting extensions extend from the foundation surface. In certain such cutting elements, the foundation surface is generally frustoconical, generally or partially dome-shaped, or other non-planar shape. Furthermore, as previously mentioned, the cutting extensions may include at least two cutting extensions that have cutting surfaces that differ in shape, height, extension angle, crest angle, or cant angle.

The cutting surfaces of the various cutting extensions (as well as the entire cutting extension itself) may be made of differing materials, in particular those having differing degrees of wear resistance, hardness and durability. The materials employed as the cutting surface, like the extension angles, extension height, cutting shapes, twist angle and cant angle may be varied to optimize the cutting element for the particular duty that is expected. For example, relatively long and relatively sharp crested cutting extensions may be included in a cutting element for particular use in soft formations. The same cutting element may include shorter and more rounded cutting extensions as being advantageous when the bit encounters harder formations. As stated, various combinations of the cutting extensions' geometric characteristics or material properties allow the bit designer abundant latitude in optimizing a particular cutting element, where the term “optimizing” includes appropriate compromises in design.

Other embodiments of the invention include a drill bit for drilling through earthen formations including a bit body, at least one rolling cone cutter rotatably mounted on the bit body, and a plurality of cutting elements mounted in the cone cutter, wherein at least one of the cutting elements includes a base portion secured in the cone cutter and a cutting portion having a plurality of cutting extensions extending from the base and being separated by valleys. The drill bit may include such a cutting element located in the nose portion of the bit where the longitudinal axis of the cutting element may be aligned with the cone axis. Alternatively, the bit may have a plurality of cutting elements with multiple cutting extensions where the elements are mounted in the nose region of the cone cutter and disposed in a circumferential row about the cone axis. The cutting extensions may vary in size, shape, extension height, extension angle, crest length, as examples.

The cutting elements and drill bit described herein provide an aggressive cutting structure and cutting element with multiple cutting extensions. At least when employed in the nose region of a bit, these embodiments, offer potential in ROP enhancement given, in particular, that the cutter's multiple cutting extensions will engage and cut the borehole bottom more times per bit revolution than, for example, a conventional chisel-shaped element having only a single cutting surface or the conventional conical cutter having only a relatively blunt cutting surface.

Thus, the embodiments described herein comprise a combination of features intended to enhance the state of the art relating to bit and cutting element design. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For an introduction to the detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is an elevation view of a rolling-cone, earth-boring bit;

FIG. 2 is a partial cross sectional view of the bit of FIG. 1 inside of a borehole;

FIG. 3 is another partial cross-sectional view of the bit of FIG. 1 inside of a borehole;

FIG. 4 is an elevation view of a cutting element in the form of an insert for use in the drill bit of FIG. 1.

FIG. 5 is a top view of the cutting element of FIG. 4.

FIG. 6 is a top view, in schematic form, showing the orientation of the crests of the cutting extensions of the cutting element shown in FIGS. 4 and 5.

FIG. 7 is a top view, in schematic form, showing the orientation of the crests of the cutting extensions in another cutting element that may be employed in the rolling cone bit of FIG. 1.

FIG. 7A is a side elevation view of the cutting element shown in FIG. 7.

FIG. 8 is a top view, in schematic form, showing the orientation of the crests of the cutting extensions in another cutting element that may be employed in the rolling cone bit of FIG. 1.

FIG. 9 is an elevation view, partly in cross-section, of the cutting element shown in FIG. 4.

FIG. 10 is an elevation view of another cutting element in the form of an insert for use in the drill bit of FIG. 1.

FIG. 11 is a top view of the cutting element of FIG. 10.

FIG. 12 is a top-view, in schematic form, showing the orientation of the crests of the cutting extensions of another cutting element for use in the bit of FIG. 1.

FIG. 13 is an elevation view, partly in cross-section, of the cutting element shown in FIG. 12.

FIG. 14 is an elevation view of another cutting element in the form of an insert for use in the drill bit of FIG. 1.

FIG. 15 is a top view of the cutting element of FIG. 14.

FIG. 16 is an elevation view of still another cutting element in the form of an insert for use in the drill bit of FIG. 1.

FIG. 17 is a top view of the cutting element of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Presently-preferred embodiments of the invention are shown and described below. These embodiments are exemplary only, and are not limiting. That is, the scope of the invention is not limited by the description of the specific embodiments described below, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims

As used herein to compare or claim particular features or characteristics (such as, for example, heights, lengths, angles) of different cutting extensions or cutting elements, the term “differs” or “different” means that the value or magnitude of the characteristic being compared varies by an amount that is greater than that resulting from accepted variances or tolerances normally associated with the manufacturing processes that are used to formulate the raw materials and to process and form those materials into a cutting element. Thus, particular characteristics selected so as to have the nominal value will not “differ,” as that term has thus been defined, even though the characteristics, if measured, would vary about the nominal value by a small amount.

In the description that follows, like parts or features are referred to throughout the specification and drawings with the same reference numerals. The drawing figures are not necessarily to scale. In the figures, certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of certain elements may be omitted in the interest of clarity and conciseness.

Referring first to FIG. 1, an earth-boring bit 30 includes a central axis 31 and a bit body 32 having a threaded section 33 on its upper end for securing the bit to the drill string (not shown). Bit 30 has a predetermined gage diameter as defined by three rolling cone cutters 34, 35, 36 which are rotatably mounted on bearing shafts (not shown) that depend from the bit body 32. The embodiments disclosed herein will be understood with a detailed description of one such cone cutter 34, with cones 35, 36 being similarly, although not necessarily identically, configured. Bit body 32 is composed of three sections, or legs 37 (two shown in FIG. 1), that are jointed together to form bit body 32.

Referring now to FIG. 2, bit 30 is shown inside a borehole 29, which includes sidewall 42, corner portion 43 and bottom 44. Cone cutter 34 is rotatably mounted on a pin or journal 38, with an axis of rotation 39 oriented generally downward and inward towards the center of bit 30. Cone cutter 34 is secured on pin or shaft 38 by ball bearings 40. Cutters 34-36 include a plurality of tooth-like cutting elements 41, for gouging and chipping away formation material to form the borehole 29.

Referring still to FIGS. 1 and 2, each cone cutter 34-36 includes a backface 45 and nose portion 46 generally opposite backface 45. Cutters 34-36 further include a frustoconical heel surface 47 that is adapted to retain cutting elements 51 that scrape or ream sidewall 42 of the borehole as cutters 34-36 rotate about borehole bottom 44. Frustoconical surface 47 is referred to herein as the “heel” surface of cutters 34-36, it being understood, however, that the same surface may be sometimes referred to by others in the art as the “gage” surface of a rolling cone cutter. Extending between heel surface 47 and nose 46 is a generally conical surface 48 adapted for supporting cutting elements 41 which gouge or crush the borehole bottom 44 as the cone cutters 34-36 rotate about the borehole.

Referring back to FIG. 1, conical surface 48 typically includes a plurality of generally frustoconical segments 49, generally referred to as “lands,” which are employed to support and secure cutting elements 41. Frustoconical heel surface 47 and conical surface 48 converge in a circumferential edge or shoulder 50. Cutting elements 41 retained in cone cutter 34 include a plurality of heel row inserts 51 that are secured in a circumferential row 52 in the frustoconical heel surface 47. Cone cutter 34 further includes a circumferential row 53 of gage inserts 54 secured to cone cutter 34 in locations along or near the circumferential shoulder 50. Cone cutter 34 further includes a plurality of inner row inserts, such as inserts 55 and 56 secured to cone surface 48 and arranged in spaced-apart inner rows 57 and 58, respectively.

Referring again to FIG. 2, heel inserts 51 generally function to scrape or ream the borehole sidewall 42 to maintain the borehole 29 at full gage and prevent erosion and abrasion of heel surface 47. Cutting elements 55 and 56 of inner rows 57 and 58 are employed primarily to gouge and crush and thereby remove formation material from the borehole bottom 44. Inner rows 57 and 58, are arranged and spaced on cone cutter 34 so as not to interfere with the inner rows on each of the other cone cutters 35, 36.

In the embodiment shown in FIGS. 1 and 2, each cone cutter 34-36 includes at least one cutting element on nose portion 46 spaced radially inward from inner rows 57 and 58, herein referred to as a nose insert 60. As cone cutters 34-36 rotate about their respective axis 39, nose inserts 60 gouge and remove the central or core portion of the borehole. As shown in FIG. 2, nose insert 60 in cone 34 is positioned such that the insert is generally aligned with cone axis 39.

Referring now to FIG. 3, bit 30 is disclosed in a borehole 29 with cone 35 shown in cross-section. All elements in FIG. 3 are identical to those disclosed in FIG. 2, with the exception that nose inserts 60 on cone 35 are now arranged in a circumferential row 62 on nose portion 46. Row 62 is disposed about cone axis 39.

A cutting element in the form of an insert 70 is shown in FIGS. 4 and 5. Insert 70 is particularly suited for use as a nose row insert 60 shown in FIGS. 2 and 3; however, it may also be employed at other locations in cone cutters 34-36. Particularly, insert 70 may also be employed as a heel row insert 51, a gage row insert 54, or inner row inserts 55, 56.

Insert 70 generally includes a base portion 71 and a cutting portion 75 connected to and extending form base 71. Base 71 includes bottom surface 72 and a generally cylindrical side surface 73 that is formed about a central, longitudinal insert axis 74. Cutting portion 75 intersects or joins base portion 71 at a generally circular junction 76. Axis 74 extends generally perpendicular to bottom 72 and a plane containing junction 76. In this embodiment, cutting portion 75 and base portion 71 are integrally-formed of tungsten carbide, although other materials and other manufacturing processes may be employed to form insert 70. Base 71, which may also be referred to as the insert's “grip,” is embedded and retained in cone 34. Cutting portion 75 is that portion of insert 70 that extends beyond the steel of the cone cutter.

Cutting portion 75 generally includes foundation surface 78. Foundation surface 78 intersects cylindrical side surface 73 of base 71 at junction 76, and extends inwardly from junction 76 toward insert axis 74 and upwardly in the direction away from bottom surface 72. In this manner, foundation surface 78 may be said to taper upwardly and away from base 71.

Cutting portion 75 further includes cutting extensions that extend from the foundation surface in a direction upward and away from base 71. In this embodiment, cutting portion 75 includes three cutting extensions 81, 82, 83 separated from one another by valleys 84, 85, 86, best shown in FIG. 5. The intersection of valleys 84-86 form a central recess or valley 87 in this embodiment.

As best shown in FIG. 4, the embodiment of insert 70 includes three distinctly-shaped cutting extensions. Cutting portion 75 includes no plane of symmetry that passes through axis 74, such that cutting portion 75 has an asymmetrical cutting surface.

Cutting extension 81 includes a generally dome-shaped cutting surface 90 which may be hemispherical or a greater or lower portion of a dome. Cutting surface 90 intersects with foundation surface 78 in a curved junction or fillet 91. Cutting extension 83 includes a generally chisel-shaped cutting surface 92, including sloping sides 93 and crest 94, which forms a crest axis 95. The chisel-shaped cutting surface 92 intersects foundation surface 98 in a rounded intersection or fillet 96. Cutting extension 82 also includes a chisel-shaped cutting surface 98 having a crest 101 that generally extends along crest axis 104. Cutting surface 98 includes sloping sides 100 that slope from crest 101 to intersect with foundation surface 78 in a rounded or radiused fillet 99. Preferably, the radius of junctions 91, 96 and 99 is selected to be not less than 0.080. As best shown in FIG. 5, crest 101 of cutting extension 82 is narrower or sharper at outer end 102 as compared to inner end 103. Further, crest 101 of cutting extension 82 is broader at both its inner and outer ends 101, 102 as compared with crest 94 on cutting extension 83.

Cutting extensions 81-83 are spaced apart from one another and separated by valleys 84-87, meaning that a planar cross-section of cutting portion 75 taken perpendicular to insert axis 74 will intersect the extensions in a plurality of spaced-apart closed figures when the cross-section is taken at at least one axial position along insert axis 74. Thus, it is understood with reference to FIG. 4 that a cross-section of insert 71 taken at plane 88 that is perpendicular to insert axis 74 will yield a cross-section having three spaced-apart closed figures, each represented by the intersection of plane 88 with the cutting surfaces 90, 98 and 92 of extensions 81, 82, 83, respectively.

In the embodiment shown in FIGS. 4 and 5, foundation surface 78 is shown to be generally conical. This and other non-planar surfaces, such as generally or partially dome-shaped, conical, hemispherical, or other curved surfaces, are preferred for foundations surface 78; however, foundation surface 78 may be generally planar in some embodiments.

In the embodiment shown in FIGS. 4 and 5, cutting extensions 81-83 extend to outermost points that fall outside of an extending projection of cylindrical side surface 73. As such, cutting extensions 81-83 have a negative draft in relation to base portion 71. A cutting portion that does not extend beyond or outside of the upward projection of the outer cylindrical side surface 73 may also be employed, and would have what may be referred to as a positive draft with respect to base portion 71. As compared to a cutting element having a cutting surface with a positive draft relative to its base, a design employing a negative draft would potentially allow a greater volume of hole bottom material to be cut with a given impact of the cutting element.

In the embodiment shown in FIGS. 4 and 5, the cutting surfaces 90, 98, and 92 of cutting extensions 81-83 are continuously contoured to avoid sharp edges or discontinuities or abrupt changes in slope. As used herein, the term “continuously contoured” refers to surfaces that can be described as having continuously curved surfaces that are free of relatively small radii that are sometimes used to break sharp edges or round off transitions between adjacent distinct surfaces. Likewise, the intersections 91, 96 and 99 likewise may be formed to be free of such small radii, such that the entire cutting portion 75 of insert 70 may be said to have a cutting surface that is continuously contoured.

The cutting elements described herein as having a generally chisel-shape and crest may take many forms. For example, cutting extensions having the chisel-shape depicted and described with reference to FIGS. 5-8 in U.S. Pat. No. 5,172,777 may be employed. The entire disclosure of U.S. Pat. No. 5,172,777 is hereby incorporated by reference.

Although the cutting surfaces of extensions 81-83 are shown and have been described as being continuously contoured, in order to illustrate certain aspects of insert 70, it is useful to refer to certain portions of the cutting extensions as having distinct boundaries that do not actually exist. Thus, for ease of explanation only, FIGS. 6-8 show top views of cutting element inserts having certain artificial boundaries superimposed in a schematic fashion. In particular, and referring to FIG. 6, a top view of insert 70 showing cutting extension 83 with crest region 97 and crest axis 95 radially disposed relative to insert axis 74. That is, crest axis 95 is substantially aligned with radius R of insert 70. Likewise, cutting extension 82 includes crest region 105 and is formed such that region 105 and crest axis 104 are radially aligned relative to insert axis 74. As shown in this embodiment, cutting extensions 82 and 83 are arranged such that crest axes 104 and 95 intersect and form an angle of intersection of approximately 120°.

Referring to FIG. 8, another embodiment is shown. Like the embodiment of FIGS. 4-6, insert 114 of FIG. 8 includes cutting extensions 81-83 as previously described. In this embodiment, however, cutting extension 83 is formed having cutting surface 116 with crest axis 95 twisted or rotated relative to its orientation shown in FIGS. 6 and 7 where axis 95 was substantially aligned with or parallel to radius R. With cutting surface 116 of FIG. 8, crest axis 95 does not pass through insert axis 74. The angle formed between crest axis 95 and radius R that passes through the midpoint MP of crest 94 forms what is described as the twist angle α. It should be understood that, in addition to either canting or rotating the cutting extension as shown in FIGS. 7 and 8, respectively, a cutting extension may be disposed such that it is both canted and twisted relative to a position in which a crest axis passes through the insert axis.

FIG. 9 illustrates other features relating to insert 71 previously described with reference to FIGS. 4-6. In particular, FIG. 9 shows insert 71 in partial cross-section with the section taken along crest axis 95 and through insert axis 74. As shown, cutting extension 83 includes an extension axis 106 that intersects insert axis 74 in an extension angle θ, which preferably is less than 60°. As used herein, the extension axis of a cutting extension may be described as the axis that passes through the midpoint of the extension's crest and that bisects the longitudinal cross-sectional area that is formed by the plane that contains the crest and that bisects the extension. Each of inserts 81-83 may include extension angles θ that are equal to one another, or they may differ. Likewise, in certain applications, it is believed advantageous to have cutting extensions 81-83 extend to different heights. As used herein, the extension height of a cutting extension is the distance measured axially from the junction 76 to the furthest point on the extension's cutting surface. As shown in FIG. 9, cutting extension 83 includes an extension height 108 that is greater than the extension height 109 of cutting extension 81.

Referring now to FIGS. 7 and 7A, another embodiment of a cutting element is shown. In this embodiment, cutting element 110 includes foundation surface 78 and cutting extensions 81, 82 as previously described. Cutting element 110 further includes cutting extension 83′ which is substantially the same as cutting extension 83 previously described. However, in this embodiment, cutting extension 83′ is canted in relation to the position of cutting extension 83 in the embodiment shown in FIGS. 4-6. More particularly, as best shown in FIG. 7A, cutting extension 83′ extends from the foundation surface 78 at a cant angle β as measured between extension axis 106′ and the insert axis 74. In the embodiment of FIGS. 4-6, cutting element 83 included a cutting extension axis 106 having a projection substantially aligned with insert axis 74. As shown in FIG. 7A, canting the cutting extension to the position represented by 83′ moves the cutting extension axis 106′ such that, when viewed from the top of the cutting element (FIG. 7), crest axis 95 is not aligned with a radius R. The axis 95 further does not pass through insert axis 74.

The embodiments thus described include features believed to enable a nose row cutting element to cut the core portion of the borehole effectively, and to do so in a variety of formation hardnesses. For example, and referring to FIG. 9, the relatively long extension of cutting extension 83 and the relatively sharp cutting surface formed by its chisel shape is believed advantageous in cutting through relatively soft formations. In somewhat harder formations, it is believed that crested cutting extension 82 will provide an advantageous blend of aggressiveness and durability, given its intermediate extension length, relative to cutting extensions 81 and 83, and given that it includes a chisel shape, albeit more rounded than the sharper chisel shape of cutting extension 83. In still harder formations, although the cutting extensions 82 and 83 may wear and thereby not provide the rapid removal of formation material as they would in softer formations, the generally rounded, dome-shaped cutting surface 90 of cutting extension 81 is believed advantageous. In particular, the dome shape provides a durable, wear-resistant cutting surface.

Additional wear-resistance may be provided to cutting extensions 81-83. In particular, some or all of the cutting surfaces of these cutting extensions may be coated with diamond or other super-abrasive material in order to optimize (which may include compromising) cutting effectiveness and/or wear-resistance. In the embodiment shown in FIGS. 4 and 5, for example, it is contemplated that only the dome-shaped cutting surface 90 of cutting extension 81 be coated with super abrasive material, with the cutting extensions 82, 83 being made entirely of tungsten carbide. In another embodiment, it may be that the cutting surfaces of all three of cutting extensions 81, 82, 83 are coated with a super abrasive.

Super abrasives are significantly harder than cemented tungsten carbide. As used herein, the term “super abrasive” means polycrystalline diamond (PCD), carbon boron nitron (CBN)thermal stable diamond (TSP), cubic boron nitride (PCBN), and any other material having a hardness of at least 2,700 Knoop (kg/mm²). As examples, PCD grades have a hardness range of about 5,000-8,000 Knoop (kg/mm²) while PCBN grades have hardnesses which fall within the range of about 2,700-3,500 Knoop (kg/mm²). By way of comparison, conventional cemented tungsten carbide grades typically have a hardness of less than 1,500 Knoop (kg/mm²).

Certain methods of manufacturing cutting elements with PDC or PCBN coatings are well known. Examples of these methods are described, for example, in U.S. Pat. Nos. 5,766,394, 4,604,106, 4,629,373, 4,694,918 and 4,811,801, the disclosures of which are all incorporated herein by this reference.

There are today a number of commercially available cemented tungsten carbide grades that have differing, but in some cases overlapping, degrees of hardness, wear resistance, compressive strength and fracture toughness. Some of such grades are identified in U.S. Pat. No. 5,967,245, the entire disclosure of which is hereby incorporated by reference. With this understanding, and referring to FIG. 4 as an example, the cutting extensions 82 and 83 may be made of tungsten carbide having differing mechanical or physical properties. In particular, in this embodiment, it is desirable that the longer and generally sharper cutting extension 83 be made of a tungsten carbide having a higher degree of toughness than the cutting extension 82. Similarly, the tungsten carbide employed in cutting extension 82 is preferably harder and more wear-resistant than the material of cutting extension 83. As a still further example, cutting extension 81 would include a substrate material beneath the diamond coating and, in this example, may be made of a carbide material that is harder and more wear-resistant than the tungsten carbide used to form cutting extension 83. Compared to the material used to form cutting extension 82, the substrate of cutting extension 81, depending upon the particular application, may be harder and more wear-resistant, but have a lower degree of facture toughness.

In another embodiment shown in FIGS. 10 and 11, cutting element 120 includes a base portion 121, axis 122, and a cutting portion 123. Cutting portion 123 intersects the base at junction 124. In this embodiment, cutting portion 123 includes foundation surface 78 and three identically configured cutting extensions 83, having the shape and structure previously described. Best shown in FIG. 11, cutting extension 83 includes a chisel-shaped cutting surface 92 including sloping sides 93, crest 94 and crest axis 95. In this embodiment, crest axis 95 of each of the cutting extensions 83 intersect with insert axis 122. It is preferred that the cutting surfaces of all cutting extensions 83 be continuously contoured.

The cutting extensions 83 may be oriented differently than shown in FIG. 11. For example, the cutting extensions 83 may be canted, twisted or both, such that in alternative orientations, the crest axis 95 of the cutting extension involved will not pass through the insert axis 122. Such adjustments in the orientation of the cutting extensions and their crests may be desirable to optimize cutting effectiveness, or durability or other characteristics. As an example, one such alternative is shown in FIG. 12, in which cutting element 127 includes cutting portion 123 which includes chisel-shaped cutting extensions 83 a, 83 b, 83 c defining asymmetrical cutting surface 126. As shown in FIG. 12, cutting extension 83 a is oriented such that crest axis 95 a extends radially and intersects insert axis 129. By contrast, cutting extension 83 b is oriented such that its crest 95 b is twisted or rotated away from being in alignment with the insert's radius, forming an angle α₁ equal to approximately 20°. Cutting extension 83 c is oriented such that crest axis 95 c is further rotated from being aligned with an insert radius, crest axis 95 c intersecting with the insert radius at an angle α₂ of approximately 40°. Varying the twist angle, as defined above, among the various cutting extensions on the insert is believed to provide the opportunity to enhance cutting effectiveness in certain formations while maintaining acceptable durability in others. In addition to varying the twist angle, the cutting extensions may likewise be canted to differing degrees.

Further still, and referring to FIG. 13, the extension height and extension angle of cutting extensions may be varied to provide enhanced durability, greater rate of penetration, or a compromise in these characteristics. For example, as shown in FIG. 13, an insert 132 is shown that is substantially similar to the insert 120 described with reference to FIGS. 10 and 11. In the embodiment of FIG. 13, however, chisel-shaped cutting extension 83 d has a greater extension height 133 than the extension height 134 of chisel-shaped cutting extension 83 e. Likewise, relative to longitudinal element axis 135, cutting extension 83 d has a first extension angle θ₁ that is less than the extension angle θ₂ of cutting extension 83 e. With these differences, extensions 83 provide an asymmetric cutting surface 136. It is believed that advantages may be obtained by employing extension angles of between approximately 0 and 60°; however, other extension angles may be employed.

Referring to FIGS. 14 and 15, another cutting element 140 is shown having a cutting portion 142 extending from a base portion 144. In this embodiment, cutting portion 142 includes three cutting extensions 82 that are substantially identical to cutting extensions 82 previously described with reference to FIGS. 4-5. In particular, each cutting extensions 82 includes a crest 101 and sloping sides 100 that intersect foundation surface 78 at fillet 99. The crest 101 is oriented such that crest axis 104 extends radially and passes through insert axis 146. The outer end 102 of each crest 101 is narrower or sharper than the inner end 103. It is believed that this cutting element will be more durable than, for example, the cutting element 120 described with reference to FIGS. 10 and 11 where relatively sharper chisel shapes are employed. As such, the insert 140 of FIGS. 14 and 15 may be advantageous in formations that are expected to be harder than those in which the embodiment of FIGS. 10 and 11 would be used.

Another embodiment is shown in FIGS. 16 and 17. Here, the cutting element 150 includes base portion 151 and cutting portion 152 having three cutting extensions 81 substantially the same as extension 81 previously described with reference to FIGS. 4 and 5. Each cutting extensions 81 includes a dome or partial dome-shaped cutting surface 90. In the embodiment shown, each cutting extension 81 is oriented so as to have the same extension angle relative to element axis 154, but the extension angle and extension height of the cutting extensions 81 may differ. Likewise, the spherical radius of curvature of each cutting surface 90 in this embodiment is substantially the same, it being understood that the spherical radius of curvature of the respective cutting surfaces may differ in other embodiments. It is believed that the insert of FIGS. 16 and 17 may best be employed in hard formations where great durability is desirable. Accordingly, in such hard formations, the cutting surface 90 of one or more cutting extensions 81 may be diamond-coated or coated with any other super abrasive material.

While the embodiments described above are shown having three cutting extensions, it should be understood that the number of cutting extensions may vary depending upon the application. Thus, for example, the cutting elements shown herein may instead be formed having two or even four or more cutting extensions.

The cutting elements described herein may be advantageously employed in the nose region of a cone cutter, or in other locations. When employed in the nose region or portion, as shown in FIGS. 1-3, the multiple cutting extensions enhance the ability of the bit to cut the central core of the borehole as compared to a bit having conventional conical or chisel-shaped cutting element with only a single cutting extension. Compared to such conventional inserts, the cutting elements described herein will contact the core portion many more times per bit revolution than a conventional, single cutting extension, cutting element. The multiple cutting extensions provide more impacts or scrapes on the hole bottom per revolution of the bit, helping to prevent core buildup. Varying the cutting surface shape of the cutting extensions, varying their height, orientation, extension angle and materials provide the bit designer with numerous design features to provide the optimum cutting structure in light of the particular formation expected to be encountered and other factors.

The following co-pending patent applications are hereby incorporated by reference in their entireties: U.S. patent application Ser. No. 10/355,493, filed Jan. 31, 2003, entitled “Multi-Lobed Cutting element For Drill Bit” and of U.S. patent application Ser. No. 10/371,388, filed Feb. 21, 2003, entitled “Drill Bit Cutting element Having Multiple Cusps.” 

1. A cutting element for a drill bit comprising: a base portion having a longitudinal axis and a cutting portion extending from said base portion; said cutting portion comprising a non-planar foundation surface extending from said base toward said axis, a plurality of cutting extensions extending from said foundation surface, and a valley between said cutting extensions.
 2. The cutting element of claim 1 wherein said plurality of cutting extensions include at least two cutting extensions having cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, twist angle and cant angle.
 3. The cutting element of claim 1 wherein said foundation surface has a shape selected from generally frustoconical and generally dome-shaped.
 4. The cutting element of claim 1 wherein said plurality of cutting extensions includes at least a first cutting extension having a first crest.
 5. The cutting element of claim 4 wherein said base includes a longitudinal axis, and wherein said first crest defines a crest axis, said first cutting extension being formed such that said first crest axis does not intersect said longitudinal axis.
 6. The cutting element of claim 4 wherein said base includes a cutting element axis, and wherein said cutting portion includes a first cutting extension having a first crest and first crest axis and a second cutting extension having a second crest and second crest axis, wherein said first crest axis forms a first angle of intersection with said element axis, and said second crest axis forms a second angle of intersection with said element axis that is different than said first angle of intersection.
 7. The cutting element of claim 1 wherein said cutting extensions include at least three cutting extensions having cutting surfaces, and wherein at least a first of said cutting surface differs in shape from a second of said cutting surfaces.
 8. The cutting element of claim 1 wherein said cutting extensions include at least a first cutting extension having a generally dome-shaped cutting surface, and a second cutting extension having a cutting surface comprising a crest.
 9. The cutting element of claim 1 wherein said plurality of cutting extensions includes at least one cutting extension having a crest with first and second ends, and wherein said first end is more narrow than said second end.
 10. The cutting element of claim 9 wherein said base includes a longitudinal axis, and wherein said second end of said crest is closer to said longitudinal axis than said first end.
 11. The cutting element of claim 1 wherein said cutting extensions comprise materials having differing mechanical properties.
 12. A cutting element for a drill bit comprising: a base portion and a cutting portion extending from said base portion; said cutting portion comprising a plurality of cutting extensions extending away from said base and valleys between said cutting extensions, at least one of said cutting extensions having a crest.
 13. The cutting element of claim 12 wherein said cutting portion comprises at least two cutting extensions having cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, cant angle and twist angle.
 14. The cutting element of claim 12 wherein said plurality of cutting extensions includes at least one cutting extension having a crest that is more narrow at a first end than a second end.
 15. The cutting element of claim 12 wherein said cutting portion further comprises a foundation surface adjacent said base having a shape selected from one of generally conical, and generally dome-shaped, said cutting extensions extending from said foundation surface.
 16. The cutting element of claim 12 wherein a first of said cutting extensions includes a dome-shaped cutting surface and wherein a second of said cutting extensions includes a cutting surface comprising a crest.
 17. The cutting element of claim 16 wherein said second cutting extension has a greater extension height than said first cutting extension.
 18. The cutting element of claim 12 wherein said cutting element includes a longitudinal axis, and wherein said crest includes a crest axis, and wherein said crest axis does not intersect said longitudinal axis.
 19. A drill bit for drilling through earthen formations, the drill bit comprising: a bit body; at least one rolling cone cutter rotatably mounted on said bit body for rotation about a cone axis, said cone cutter including a backface, a nose portion generally opposite said backface, and a generally conical surface between said nose portion and said backface; a plurality of cutting elements mounted in said cone cutter, at least one of said cutting elements comprising a base portion secured within said cone cutter and a cutting portion extending from said base portion, said cutting portion comprising a plurality of cutting extensions, said cutting extensions being separated by valleys.
 20. The drill bit of claim 19 wherein said at least one cutting element is mounted in said cone cutter in a position selected from one of said nose portion and said generally conical surface.
 21. The drill bit of claim 19 wherein said at least one cutting element further comprises a foundation surface extending from said base portion and, wherein, said plurality of cutting extensions extend from said foundation surface, said foundation surface being one of generally flat, generally frustoconical and generally dome-shaped.
 22. The drill bit of claim 19 wherein at least two of said cutting extensions include cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, twist angle and cant angle.
 23. The drill bit of claim 19 wherein at least one of said cutting extensions includes a cutting surface comprising a crest.
 24. The cutting element of claim 19 wherein said at least one cutting element includes a first cutting extension having a cutting surface that is generally dome shaped and a second cutting extension having a cutting surface that includes a crest.
 25. The cutting element of claim 24 wherein said second cutting extension includes an extension height that is greater than the extension height of said first cutting extension.
 26. The drill bit of claim 19 wherein said at least one cutting element includes a longitudinal axis, and wherein said cutting extensions form extension angles with said longitudinal axis, and wherein said extension angles of at least two of said cutting extensions differ.
 27. The drill bit of claim 19 wherein said at least one cutting element includes cutting extensions that include cutting surfaces that differ in at least one mechanical property selected from hardness, wear-resistance, and fracture toughness.
 28. The drill bit of claim 22 wherein said at least one cutting element includes a longitudinal axis, and wherein said cutting element is mounted in said cone cutter such that said element axis is substantially aligned with said cone axis.
 29. The drill bit of claim 28 wherein said plurality of cutting extensions includes at least a first cutting extension having a crested cutting surface and at least a second cutting element including a generally dome-shaped cutting surface.
 30. A drill bit for drilling through earthen formations, the drill bit comprising: a bit body; at least one rolling cone cutter rotatably mounted on said bit body for rotation about a cone axis, said cone cutter including a backface, a nose portion generally opposite said backface, and a generally conical surface between said nose portion and said backface; at least one nose cutting element mounted in said nose portion, said nose cutting element comprising a base portion having an outer surface secured within said cone cutter, an element axis, and a cutting portion extending from said base portion, said cutting portion comprising a plurality of cutting extensions separated by valleys.
 31. The drill bit of claim 30 wherein said nose cutting element is mounted in said cone with said element axis generally aligned with said cone axis.
 32. The drill bit of claim 30 further comprising a plurality of said nose cutting elements retained in said cone cutter in a circumferential row that is disposed about said cone axis. 